Method and apparatus for color image forming capable of effectively forming a quality color image

ABSTRACT

A maintenance pattern forming method includes conveying, generating, and forming. The conveying conveys a transfer member on a surface of a conveying member such that there is a spacing area between two adjacent transfer members on the surface of the conveying member. The generating generates a timing signal for at least one of a plurality of colors formed by a color image forming apparatus. The forming forms at least one of a process control pattern, a position adjustment pattern, and a blade curl suppression pattern onto the spacing area based on the timing signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent specification is based on Japanese patent application, No.JP2005-346298 filed on Nov. 30, 2005 in the Japan Patent Office, theentire contents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for color imageforming, and more particularly to a method and apparatus for color imageforming capable of effectively forming a quality color image bysimplifying maintenance pattern management.

2. Discussion of the Background

As a background, the color image forming apparatus described in JapanesePatent Application Laid-Open No. 2005-91901 is known. The color imageforming apparatus described in Japanese Patent Application Laid-Open No.2005-91901 (hereinafter “background image forming apparatus”) formsdensity detection patterns on a non-image-formation area of a conveyorbelt during continuous printing. The background color image formingapparatus then changes image forming conditions of position detectionpatterns based on detection results of the density detection patterns.Thus, a positional displacement, which may be caused when toner imagesof different colors are superposed upon each other, can be suitablycorrected while image formation efficiency is increased.

More specifically, in the background color image forming apparatus, theposition detection patterns are formed on the conveyor belt with imageforming mechanisms of respective colors, and are detected with an imageposition detector. Then, based on results detected with the imageposition detector, displacement correction processing is executed tocorrect the positional displacement.

For the displacement correction processing, density detection patternsare formed on a non-image-formation area of the conveyor belt whileimage formation is not performed onto a transfer sheet. Then, thedensity detection patterns are detected with the image positiondetector. Based on results detected with the image position detector,image forming conditions are determined to form the position detectionpatterns with the image forming mechanisms during execution of thedisplacement correction processing.

In the background color image forming apparatus according to the abovepatent document, a system controller starts positional displacementcorrection when it receives a permission notification for starting thepositional displacement correction from a position adjustmentcontroller. The system controller initially detects a density detectionpattern formed on a non-image-formation area of the conveyor belt. Thedensity detection pattern is detected with a reflected light sensor ofthe image position detector.

However, the above patent document does not describe details relating toa position and a timing at which the density detection pattern isformed. In fact, particular consideration is not paid to the positionand timing at which the non-image-area density detection pattern isformed.

SUMMARY OF THE INVENTION

This patent specification describes a maintenance pattern forming methodwhich can effectively form a quality color image by simplifyingmaintenance pattern management. In one example, a maintenance patternforming method includes the steps of conveying, generating, and forming.The conveying step conveys a transfer member on a surface of a conveyingmember such that there is a spacing area between two adjacent transfermembers. The generating step generates a timing signal for at least oneof a plurality of colors formed by the color image forming apparatus.The forming step forms at least one pattern onto the spacing area basedon the timing signal. The pattern can be, but is not limited to, atleast one of a process control pattern, a position adjustment pattern,or a blade curl suppression pattern.

This patent specification further describes a novel color image formingapparatus which can effectively form a quality color image bysimplifying maintenance pattern management. In one embodiment, a colorimage forming apparatus includes a conveying member, a plurality ofimage carrying members, a signal generator, and a pattern formationmechanism. The conveying member has a surface to convey a transfermember, the surface including a spacing area between two adjacenttransfer members. The plurality of image carrying members are arrangedin tandem and carry images. The images are transferred onto the transfermember conveyed by the conveying member. The signal generator generatesa timing signal for at least one of a plurality of colors formed by thecolor image forming apparatus. The pattern formation mechanism forms apattern on the spacing area based on the timing signal. The pattern canbe, but is not limited to, at least one of a process control pattern, aposition adjustment pattern, or a blade curl suppression pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a diagram illustrating a schematic configuration of a colorimage forming apparatus according to one embodiment of the presentinvention;

FIG. 2 is an explanatory diagram illustrating a configuration to detect,with a detection sensor unit, process control patterns and positionadjustment patterns of respective colors formed on a conveyor belt;

FIG. 3 is a block diagram illustrating a configuration of a controlcircuit to perform position adjustment processing and process controlprocessing;

FIG. 4 is a timing chart illustrating timing of image formation in asub-scanning direction in the color image forming apparatus of FIG. 1;and

FIG. 5 is a schematic diagram of the conveyor belt and thephotosensitive drum of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In describing preferred embodiments illustrated in the drawings,specific terminology is employed for the sake of clarity. However, thedisclosure of this patent specification is not intended to be limited tothe specific terminology so selected and it is to be understood thateach specific element includes all technical equivalents that operate ina similar manner. Referring now to the drawings, wherein like referencenumerals designate identical or corresponding parts throughout theseveral views, particularly to FIG. 1, an image forming apparatus 100according to an exemplary embodiment of the present invention isdescribed.

As illustrated in FIG. 1, the image forming apparatus 100 includes aconveyor belt 2, a drive roller 3, a driven roller 4, a sheet feed tray5, an optical write unit 8, a fuser 13, a detection sensor 14, and acleaner 15. The image forming apparatus 100 also includes an imageforming mechanism 101 m, an image forming mechanism 101 c, an imageforming mechanism 101 y, and an image forming mechanism 101 k.

The image forming mechanism 101 m has a photosensitive drum 6 m, acharger 7 m, a developer 9 m, a photosensitive drum cleaner 10 m, and atransfer unit 12 m. The other image forming mechanisms 101 c, 101 y, and101 k have a similar configuration to the image forming mechanism 101 m.

The conveyor belt 2 is stretched between the drive roller 3 that isrotationally driven and the driven roller 4 that is dependently driventhereby. The conveyor belt 2 is rotated by rotation of the drive roller3 to convey a transfer sheet 1. The sheet feed tray 5 for storing thetransfer sheet 1 is provided below the conveyor belt 2.

The image forming mechanisms 101 m, 101 c, 101 y, and 101 k are arrangedin tandem along the conveyor belt 2. The image forming mechanisms 101 m,101 c, 101 y, and 101 k form images in magenta (m), cyan (c), yellow(y), and black (k) colors, respectively. Although the image formingmechanisms 101 m, 101 c, 101 y, and 101 k are arranged in the order inFIG. 1, the arrangement of the present invention is not limited to theorder, and other arbitrary orders may be applicable.

The optical write unit 8 is provided above the image forming mechanisms101 m, 101 c, 101 y, and 101 k. The optical write unit 8 exposessurfaces of the photosensitive drums 6 m, 6 c, 6 y, and 6 k with laserbeams 11 m, 11 c, 11 y, and 11 k, respectively, according to the imagecolor. The optical write unit 8 also includes a write control unit 8 adescribed later.

In the image forming mechanism 101 m, the photosensitive drum 6 m isarranged at a position surrounding by the charger 7 m, the developer 9m, the transfer unit 12 m, and the photosensitive drum cleaner 10 m. Thephotosensitive drum 6 m serves as a photosensitive member on which anelectrostatic latent image is formed.

The charger 7 m uniformly charges the surface of the photosensitive drum6 m. The optical write unit 8 forms an electrostatic latent image withthe laser beam 11 m on the surface of the photosensitive drum 6 m.

The developer 9 m develops the electrostatic latent image with magentacolor toner to form a magenta toner image on the surface of thephotosensitive drum 6 m. The transfer unit 12 m transfers the magentatoner image to the transfer sheet 1. The photosensitive drum cleaner 10m removes excess toner remaining on the surface of the photosensitivedrum 6 m.

The units in the other image forming mechanisms 101 c, 101 y, and 101 khave a similar arrangement to the units in the image forming mechanism101 m. Furthermore, the units in the other image forming mechanisms 101c, 101 y, and 101 k operate in a similar manner to the units in theimage forming mechanism 101 m to superimposingly form toner images ofcyan, yellow, and black, respectively, onto the magenta toner image ofthe transfer sheet 1.

The fuser 13 is arranged at a position spaced from the conveyor belt 2on a downstream side in a conveyance direction of the transfer sheet 1.After the transfer sheet 1 is separated from the conveyor belt 2, thefuser 13 fixes the toner images on the transfer sheet 1.

The detection sensor 14 is arranged at a position opposed to theconveyor belt 2, and detects a position adjustment pattern and a processcontrol pattern on the conveyor belt 2.

The cleaner 15 is also arranged at a position opposed to the conveyorbelt 2, and removes the position adjustment pattern and the processcontrol pattern detected with the detection sensor 14.

Upon the start of image formation, one transfer sheet 1 at the top ofthe transfer sheets 1 stored in the sheet feed tray 5 is fed to theconveyor belt 2, which is being rotated in a direction indicated by anarrow A in FIG. 1. Then, the transfer sheet 1 is electrostaticallyattracted to the conveyor belt 2, and is conveyed to the image formingmechanism 101 m.

In the image forming mechanism 101 m, the surface of the photosensitivedrum 6 m is uniformly charged with the charger 7 m. Then, the opticalwrite unit 8 emits the laser beam 11 m to form an electrostatic latentimage on the surface of the photosensitive drum 6 m.

The developer 9 m develops the resultant electrostatic latent image withmagenta toner to form a magenta toner image on the photosensitive drum 6m. When the transfer sheet 1 is conveyed to a transfer position at whichthe transfer sheet 1 on the conveyor belt 2 contacts the photosensitivedrum 6 m, the transfer unit 12 m transfers the magenta toner image ontothe transfer sheet 1.

Thus, the image of a single magenta color is formed on the transfersheet 1. Then, the photosensitive drum cleaner 10 m removes excess tonerremaining on the surface of the photosensitive drum 6 m. Thereby, thephotosensitive drum 6 m becomes ready for a following image formation.

Subsequently, the transfer sheet 1 that has been subjected to thetransfer of the magenta toner image is conveyed to the image formingmechanism 101 c with the conveyor belt 2.

Similar to the image forming mechanism 101 m, the image formingmechanism 101 c forms a cyan toner image on the surface of thephotosensitive drum 6 c. The transfer unit 12 c superimposinglytransfers the cyan toner image onto the transfer sheet 1.

The transfer sheet 1 is then conveyed to the image forming mechanism 101y, and subsequently the image forming mechanism 101 k.

Similar to the image forming mechanisms 101 m and 101 c, the imageforming mechanism 101 y and the image forming mechanism 101 k form ayellow toner image and a black toner image on the photosensitive drums 6y and 6 k, respectively. Then, the transfer units 12 y and 12 ksuperimposingly transfer the yellow toner image and the black tonerimage, respectively, onto the transfer sheet 1 that has been subjectedto the transfer of the magenta toner image.

After passing through the image forming mechanism 101 k, the transfersheet 1, which has a full-color toner image, is separated from theconveyor belt 2, and is moved to the fuser 13. The fuser 13 fixes thefull-color toner image on the transfer sheet 1, and then the transfersheet 1 is ejected.

Incidentally, the tandem-type image forming method as described above isgenerally called a direct transfer method, in which a toner image isdirectly transferred to a transfer sheet. In addition, an indirecttransfer method may be used for the tandem-type image forming apparatus.In the indirect transfer method, a full-color image to be transferred istemporarily formed on an intermediate transfer belt, and then theresultant full-color image is transferred to a transfer sheet.

After the ejection of the transfer sheet 1, the detection sensor 14arranged at a position opposed to the conveyor belt 2 detects a positionadjustment pattern and a process control pattern. If the positionadjustment pattern or the process control pattern is found, the cleaner15 removes the position adjustment pattern or the process controlpattern after completion of the detection.

Next, referring to FIG. 2, a configuration to detect the positionadjustment pattern and the process control pattern with the detectionsensor 14 of the present embodiment is described.

As illustrated in FIG. 2, the detection sensor 14 includes positionadjustment pattern sensors 16, 17, and 18, and process control patternsensors 22, 23, 24, and 25.

The position adjustment pattern sensors 16, 17, and 18 are arranged at ascanning start position, a central position, and a scanning endposition, respectively, in a main scanning direction, which is adirection indicated by an arrow B in FIG. 2. The position adjustmentpattern sensors 16, 17, and 18 detect position adjustment patterns 19,20, and 21, respectively.

The position adjustment patterns 19, 20, and 21 are formed for eachcolor at three positions on the conveyor belt 2 corresponding to thepositions at which the position adjustment pattern sensors 16, 17, and18 are arranged. Each of the position adjustment patterns 19, 20, and 21is formed of a combination of black (k), cyan (c), magenta (m), andyellow (y) patterns being parallel to the main scanning direction andblack, cyan, magenta, and yellow patterns being inclined at anapproximately 45 degree angle to the main scanning direction.

The process control pattern sensors 22, 23, 24, and 25 are provided inthe detection sensor 14, separately from the position adjustment patternsensors 16, 17, and 18. The process control pattern sensors 22, 23, 24,and 25 detect process control patterns 26 k, 27 c, 28 m, and 29 y ofblack, cyan, magenta, and yellow colors, respectively.

Accordingly, the process control patterns 26 k, 27 c, 28 m, and 29 y areformed at positions in parallel with the process control pattern sensors22, 23, 24, and 25, respectively.

For position adjustment control, skew from a standard color (e.g. blackin the present embodiment), registration displacement in a sub-scanningdirection, registration displacement in the main scanning direction, andmagnification error in the main scanning direction can be measured.

For example, when a positional displacement due to magnification erroris detected with the position adjustment pattern sensors 16, 17, and 18,an image formation process is controlled so that a following image isshifted by half of a maximum amount of the detected displacement in adirection opposite to a direction of the displacement. Thereby, thedisplacement amount can be corrected to a negligible level.

Furthermore, since three points in the main scanning direction aremeasured in the detection, a scanning line distortion can also bedetected. Therefore, the registration displacement in the sub-scanningdirection can optimally be corrected.

CPU 45, which will be described in greater detail later, can performposition adjustment control by calculating various displacement amountsand correction amounts and instructing to execute corrections.

On the other hand, for process control of image formation, apredetermined calculation is executed based on detection results withthe position adjustment pattern sensors 16, 17, and 18, and the processcontrol pattern sensors 22, 23, 24, and 25. Then, a condition of theimage forming process, such as charging, development, and transfer, ischanged according to the calculation result.

The positional displacement correction and the process control asdescribed above may be executed with an instruction from an operationmenu or a utility menu of the image forming apparatus 100, or a menu ofa printer driver thereof. Alternatively, the positional displacementcorrection and the process control may be automatically executedaccording to a predetermined execution condition, such as an amount oftime elapsed with the power of the image forming apparatus 100 turnedon, an accumulated number of printed sheets, or a temperature increaseamount of a portion (not illustrated) in the image forming apparatus100.

Next, referring to FIG. 3, a configuration of a controller 200 toperform processing of the position adjustment and the process control isdescribed.

The controller 200 includes an input-output interface (I/F) 30, amultiplexer (MUX) 31, a multiplexer (MUX) 35, an analog-to-digitalconverter (A/D) 32, an analog-to-digital converter (A/D) 36, a controlcircuit 33, a control circuit 37, a demultiplexer (DMUX) 38, a low passfilter circuit (LPF) 39, a low pass filter circuit (LPF) 40, a low passfilter circuit (LPF) 41, an edge detection circuit 42, an edge detectioncircuit 43, an edge detection circuit 44, a register 34, a CPU (centralprocessing unit) 45, a ROM (read only memory) 46, and a PAM (randomaccess memory) 47.

Below, a control configuration of the controller 200 together with inputand output of signal is described.

For processing of the process control, voltage signals detected with theprocess control pattern sensors 22, 23, 24, and 25 are input via theinput-output interface 30 to the multiplexer 31.

The multiplexer 31 selects a sensor channel for the voltage signals, andoutputs the voltage signal of the selected sensor channel to theanalog-to-digital converter circuit 32. The analog-to-digital convertercircuit 32 performs analog-to-digital conversion on the voltage signalof the selected sensor channel.

At this time, the control circuit 33 controls the multiplexer 31 toperform the sensor channel selection only during pattern formation. Thecontrol circuit 33 also controls the analog-to-digital converter circuit32 to perform the analog-to-digital conversion only during patternformation.

Then, the voltage signal digitally converted in the analog-to-digitalconverter circuit 32 is output to the register 34, and is storedtherein. Based on the digitally converted voltage signal, the CPU 45performs a calculation and changes a setting to change a condition ofthe image forming process, such as charging, development, and transfer.At this time, the CPU 45 executes the process control in accordance witha control program stored in the ROM 46, while using the RAM 47 as a workarea.

On the other hand, for the position adjustment processing, voltagesignals detected with the position adjustment pattern sensors 16, 17,and 18 are input via the input-output interface 30 to the multiplexer35.

The multiplexer 35 selects a sensor channel for the voltage signals, andoutputs the voltage signal of the selected sensor channel to theanalog-to-digital converter circuit 36. The analog-to-digital convertercircuit 36 performs analog-to-digital conversion on the voltage signalof the selected sensor channel.

At this time, the control circuit 37 controls the multiplexer 35 toperform the sensor channel selection only during pattern formation. Thecontrol circuit 37 also controls the analog-to-digital converter circuit36 to perform the analog-to-digital conversion only during patternformation.

Then, the voltage signal digitally converted in the analog-to-digitalconverter circuit 36 is output to the demultiplexer 38. Thedemultiplexer 38 selects one output destination of the digitallyconverted voltage signal from among the low pass filter circuits 39, 40,and 41, which are prepared for respective channels of the positionadjustment pattern sensors 16, 17, and 18. The selected one of the lowpass filter circuits 39, 40, and 41 receives the voltage signal, andcuts off a high frequency component thereof, thereby facilitatingaccurate recognition of pattern position in a following stage.

In the following stage, the edge detection circuits 42, 43, and 44 areprovided for comparing a waveform of the voltage signal with apredetermined threshold voltage. The edge detection circuits 42, 43, and44 extract a rise point and a fall point of the waveform, recognize amidpoint between the two points as a central position of the pattern,and store such data into the register 34.

Then, based on the data stored in the register 34, the CPU 45 performs acalculation and changes a setting to change a process condition andexecute the position adjustment. The CPU 45 also performs suchcalculation and setting control in accordance with the control programstored in the ROM 46, while storing calculation data and setting datainto the RAM 47.

The CPU 45 executes the above setting to change the process conditionand the position adjustment in the write control unit 8 a and a processunit via the input-output interface 30. Incidentally, the input-outputinterface 30, the ROM 46, and the RAM 47 are connected to one anothervia the address bus 48 and the data bus 49.

The write control unit 8 a controls the exposure process of the opticalwrite unit 8 based on the setting executed by the CPU 45. The processunit, which includes the image forming mechanisms 101 m, 101 c, 101 y,and 101 k, also performs image formation based on the setting executedby the CPU 45.

Furthermore, through changing setting values in the register 34, the CPU45 performs start and stop of sampling, and switching of the sensorchannels used for the analog-to-digital conversion, via the controlcircuit 33 and the control circuit 37. The CPU 45 also performs changeof the frequencies to be cut off in the low pass filter circuits 39, 40,and 41, and setting of each threshold voltage in the edge detectioncircuit 42, 43, and 44.

Moreover, another aspect of signal processing for the positionadjustment control executed in the controller 200 illustrated in FIG. 3includes the low pass filter circuits 39, 40, and 41 performingproduct-sum calculations to select the sensor channel. In addition, theedge detection circuits 42, 43, and 44 execute calculations to compare awaveform of the voltage signal, which has been obtained after theanalog-to-digital conversion and the cut-off, with a predeterminedthreshold voltage. The edge detection circuits recognize a point of thewaveform at which the voltage signal first falls below the thresholdvoltage as a fall point (i.e. an edge portion) of the pattern, recognizea point of the waveform at which the voltage signal first rises abovethe threshold voltage as a rise point (i.e. another edge portion) of thepattern, and recognize a midpoint between the rise point and the fallpoint as a central position of the pattern.

Next, referring to FIG. 4, a pattern forming method of the presentembodiment is described. In the pattern forming method, a negation edgeE of an image area signal in a sub-scanning direction, also referred toas a “sub-scan image area signal,” is used as a reference point ofpattern formation.

FIG. 4 is a timing chart illustrating a timing of image formation in thesub-scanning direction according to the present embodiment. Morespecifically, FIG. 4 illustrates a timing of image formation incontinuous printing, during which respective images of magenta, cyan,yellow, and black colors are continuously formed on a plurality of thetransfer sheets 1.

In FIG. 4, N−1, N, N+1, and N+2 represent page numbers of the transfersheets 1 subjected to the image formation. Furthermore, S represents aspacing area between two adjacent transfer sheets conveyed on theconveyor belt 2 and across the width of the conveyor belt 2.

FGATE_M, FGATE_C, FGATE_Y, and FGATE_K represent sub-scan image areasignals of magenta, cyan, yellow, and black, respectively, which aregenerated by the write control unit 8 a of FIG. 1. FGATE_M, FGATE_C,FGATE_Y, and FGATE_K sequentially become active low in accordance withtime intervals approximately corresponding to spacing intervals amongthe photosensitive drums 6 m, 6 c, 6 y, and 6 k. While each of thesub-scan image area signals is in the active low state, the opticalwrite unit 8 emits the laser beam corresponding to the image color, andforms an electrostatic latent image on each of the photosensitive drums6 m, 6 c, 6 y, and 6 k.

Then, for example, as illustrated in FIG. 4, if executing a positionaldisplacement correction after printing of the Nth page is determinedduring a position adjustment operation, formation of a positionadjustment pattern for each color is started at a time P when apredetermined time X has elapsed from a negation edge E of a sub-scanimage area signal for each color. At this time, the position adjustmentpattern for each color is formed on the spacing area S.

In this regard, assertion and negation timings of each of the sub-scanimage area signals, FGATE_M, FGATE_C, FGATE_Y, and FGATE_K, aredetermined according to count information of a number of a horizontalsynchronizing signal (not illustrated). Furthermore, the formation ofthe position adjustment pattern is started according to countinformation of a number of delay lines from the negation edge E of thesub-scan image area signal for each color. The counting of the number ofthe horizontal synchronizing signal and the number of delay lines areperformed by the write control unit 8 a.

Incidentally, the spacing area S in the sub-scan image area signals ofrespective colors, FGATE_M, FGATE_C, FGATE_Y, and FGATE_K, has aconsiderably short time length compared with the transfer sheet.

Thus, by using the negation edge E of the sub-scan image area signal asa reference point of the pattern formation, the position adjustmentpattern can be formed at a constant timing, regardless of the size ofthe transfer sheet 1.

Furthermore, management of the position adjustment operation can besimplified, and the reliability of the image forming apparatus 100 maybe increased. Moreover, the required bit number for the countinformation of delay lines may be reduced.

In addition to the position adjustment pattern as described above, forexample, a process control pattern, a blade curl suppression pattern tosuppress curling of a cleaning blade in the cleaner 15 of FIG. 1, andother patterns may be formed according to the pattern forming method.

All of the position adjustment pattern, the process control pattern, andthe blade curl suppression pattern can be formed together on the spacingarea S. In such an embodiment, all the patterns need to be properlyformed so as to achieve full performance thereof.

Moreover, the position adjustment or the process control may berequested when image formation is not performed onto the transfer sheet1, for example, when the image forming apparatus 100 is in a stand-bymode.

Also, in such a case, the control operation of the position adjustmentpattern need to be executed. Therefore, another sub-scan image areasignal is created for each color, so that each of the sub-scan imagearea signals, FGATE_M, FGATE_C, FGATE_Y, and FGATE_K forms two lines foran extremely short time. Then, another position adjustment pattern isformed based on a negation edge E of the second sub-scan image areasignal.

Thus, the management method to control the position adjustment patterndoes not need to be changed between when continuous printing is executedand when image formation onto transfer sheet 1 is not executed.Accordingly, the control operation of the position adjustment patterncan be simplified, and the reliability of the image forming apparatus100 may be increased.

Finally, referring to FIG. 5, the blade curl suppression pattern and acontrol operation to suppress curling of the cleaning blade aredescribed.

FIG. 5 is a schematic diagram of the conveyor belt 2 and thephotosensitive drum 6 m of FIG. 1. The photosensitive drum 6 m isseparately illustrated below the conveyor belt 2 for clarity. Thecleaning blade in the cleaner 15, not illustrated in FIG. 5, is arrangedat the position opposed to the conveyance belt 2 as illustrated in FIG.1.

In FIG. 5, R2 represents a sheet conveyance area, on which a transfersheet may be attached to be conveyed, and R1 and R3 represent marginareas thereof.

A curl suppression toner pattern 50 is formed on the conveyor belt 2 andis supplied to the cleaning blade. Thereby, the curl suppression tonerpattern 50 serves as a lubricant to suppress curling of the cleaningblade, which may be caused by a frictional force between the cleaningblade and the conveyor belt 2.

More specifically, the curl suppression toner pattern 50 is formed onthe spacing area S (described above with reference to FIG. 4) of theconveyor belt 2, once a predetermined print volume has been reached. Atthis time, the curl suppression toner pattern 50 is formed based on anegation edge E of a sub-scan image area signal of each color, asdescribed above.

Also, the curl suppression toner pattern 50 is formed so as to have amaximum width W of image area of the photosensitive drum 6 m. However,when an electrostatic latent image on the photosensitive drum 6 m isdeveloped as a toner image with the developer 9 m, excess toner may beattached to a non image area of the photosensitive drum 6 m.Furthermore, as illustrated in FIG. 5, when the maximum width W of imagearea of the photosensitive drum 6 m is larger than the width of atransfer sheet 1, the excess toner attached on the non image area of thephotosensitive drum 6 m is transferred onto the transfer sheet 1 andadditionally onto the conveyor belt.

Consequently, a toner amount attached on the sheet conveyance area R2 issmaller than a toner amount attached on the margin area R1 or the marginarea R3, approximated by the excess toner amount transferred onto thetransfer sheet 1.

Therefore, to equalize the toner amount differences among the marginarea R1, the sheet conveyance area R2, and the margin area R3, an imagesize of the curl suppression toner pattern 50 is changed for each area.

Specifically, the size of the transfer sheet 1 is detected with a sheetsize detector (not illustrated). Then, an irradiation time of the laserbeam for writing the curl suppression toner pattern 50 onto each of themargin areas R1 and R3 is changed according to signals from the CPU 45.Thereby, the image size of the curl suppression toner pattern 50 iscontrolled according to the area.

The image size of the curl suppression toner pattern 50 on the sheetconveyance area R2 may be increased to a level at which the blade curlcan be suppressed, corresponding to the size of the transfer sheet 1.Alternatively, the image size of the curl suppression toner pattern 50on the margin areas R1 and R3 may be decreased to a level at which acleaning failure is not caused.

Thus, the toner amounts attached on the margin area R1, the sheetconveyance area R2, and the margin area R3 can be equalized, andthereby, the blade curl and the cleaning failure can be suppressed.

This invention may be conveniently implemented using a conventionalgeneral purpose digital computer programmed according to the teachingsof the present specification, as will be apparent to those skilled inthe computer art. Appropriate software coding can readily be prepared byskilled programmers based on the teachings of the present disclosure, aswill be apparent to those skilled in the software art. The presentinvention may also be implemented by the preparation of applicationspecific integrated circuits or by interconnecting an appropriatenetwork of conventional component circuits, as will be readily apparentto those skilled in the art.

Numerous additional modifications and variations are possible in lightof the above teachings. It is therefore to be understood that within thescope of the appended claims, the disclosure of this patentspecification may be practiced otherwise than as specifically describedherein.

1. A maintenance pattern forming method for use in a color image formingapparatus, comprising: conveying a plurality of transfer members on asurface of a conveying member such that there is a spacing area on thesurface of the conveying member between at least two adjacent transfermembers; generating a timing signal for at least one of a plurality ofcolors formed by the color image forming apparatus; and forming at leastone maintenance pattern on the spacing area based on the timing signal.2. The maintenance pattern forming method according to claim 1, whereina timing signal is generated for each of the plurality of colors formedby the color image forming apparatus capable of indicating the spacingarea in image forming.
 3. The maintenance pattern forming methodaccording to claim 2, wherein the at least one maintenance pattern is atleast one of a process control pattern, a position adjustment pattern,or a blade curl suppression pattern.
 4. The maintenance pattern formingmethod according to claim 3, wherein the timing signal for each of theplurality of colors includes a sub-scan image area signal indicating aneffective image area in a sub-scanning direction on the conveyingmember.
 5. The maintenance pattern forming method according to claim 4,wherein the forming of at least one of the process control pattern, theposition adjustment pattern, or the blade curl suppression pattern isstarted after a predetermined time has elapsed from a negation timing ofthe sub-scan image area signal.
 6. The maintenance pattern formingmethod according to claim 5, further comprising: providing a counter tocount a number of lines in order to determine that the predeterminedtime has elapsed from the negation timing of the sub-scan image areasignal.
 7. The maintenance pattern forming method according to claim 3,further comprising: performing the forming of at least one of theprocess control pattern, the position adjustment pattern, or the bladecurl suppression pattern while each operation of process control,position adjustment, or blade curl suppression is executed independentlyof one another and separately from an image forming operation onto thetransfer member.
 8. A color image forming apparatus, comprising: aconveying member having a surface configured to convey a plurality oftransfer members, the surface including a spacing area between at leasttwo adjacent transfer members on the surface of the conveying member; aplurality of image carrying members that are arranged in tandem,configured to carry images and configured to transfer the images ontothe transfer member conveyed by the conveying member; a signal generatorconfigured to generate a timing signal for at least one of a pluralityof colors formed by the color image forming apparatus; and a patternformation mechanism configured to form a maintenance pattern on thespacing area based on the timing signal.
 9. The color image formingapparatus according to claim 8, wherein a timing signal is generated foreach of the plurality of colors formed by the color image formingapparatus capable of indicating the spacing area in image forming. 10.The color image forming apparatus according to claim 9, wherein the atleast one maintenance pattern is at least one of a process controlpattern, a position adjustment pattern, or a blade curl suppressionpattern.
 11. The color image forming apparatus according to claim 10,wherein the timing signal for each of the plurality of colors includes asub-scan image area signal indicating an effective image area in asub-scanning direction on the conveying member.
 12. The color imageforming apparatus according to claim 11, wherein at least one of theprocess control pattern, the position adjustment pattern, or the bladecurl suppression pattern is started to be formed after a predeterminedtime has elapsed from a negation timing of the sub-scan image areasignal.
 13. The color image forming apparatus according to claim 12,wherein a counter to count a number of lines is provided to determinethat the predetermined time has elapsed from the negation timing of thesub-scan image area signal.
 14. The color image forming apparatusaccording to claim 10, wherein the forming of at least one of theprocess control pattern, the position adjustment pattern, or the bladecurl suppression pattern is performed while each operation of processcontrol, position adjustment, or blade curl suppression is executedindependently of one another and separately from an image formingoperation onto the transfer member.
 15. A color image forming apparatus,comprising: means for conveying a plurality of transfer members on asurface, the surface including a spacing area between at least twoadjacent transfer members on the surface of the means for conveying;means for carrying images, which are transferred onto the transfermembers conveyed by the means for conveying a plurality of transfermembers; means for generating a timing signal for at least one of aplurality of colors formed by the color image forming apparatus; andmeans for forming a maintenance pattern on the spacing area based on thetiming signal.
 16. The color image forming apparatus according to claim15, wherein a timing signal is generated for each of the plurality ofcolors formed by the color image forming apparatus capable of indicatingthe spacing area in image forming.
 17. The color image forming apparatusaccording to claim 16, wherein the at least one maintenance pattern isat least one of a process control pattern, a position adjustmentpattern, or a blade curl suppression pattern on the spacing area. 18.The color image forming apparatus according to claim 17, wherein thetiming signal for each of the plurality of colors includes a sub-scanimage area signal that indicates an effective image area in asub-scanning direction on the means for conveying the plurality oftransfer members.
 19. The color image forming apparatus according toclaim 18, wherein the forming of at least one of the process controlpattern, the position adjustment pattern, or the blade curl suppressionpattern is started after a predetermined time has elapsed from anegation timing of the sub-scan image area signal.
 20. The color imageforming apparatus according to claim 19, wherein a counter to count anumber of lines is provided to determine that the predetermined time haselapsed from the negation timing of the sub-scan image area signal. 21.The color image forming apparatus according to claim 17, wherein theforming of at least one of the process control pattern, the positionadjustment pattern, or the blade curl suppression pattern is performedwhile each operation of process control, position adjustment, or bladecurl suppression is executed independently of one another and separatelyfrom an image forming operation onto the transfer member.